Mild detonating fuze (MDF) is a metal clad linear explosive usually drawn or extruded in a round configuration. Grain sizes can vary from 2.5 gr/ft to 100 gr/ft, and the metal sheath can be aluminum, tin, lead or silver. The diameter of MDF ranges from 40 mils or smaller to 250 mils or larger.
D. Smith, U.S. Pat. No. 6,561,101, shows a typical application where a length of MDF is used to delay a detonation after an input. The MDF is placed in a groove spiraling around the exterior surface of a metal case of a device. An electrically controlled igniter ignites one end of the MDF and the other end ignites an actuator. The length of MDF is chosen to provide a predetermined delay between ignition and actuation, the delay being a function of the length of MDF and the velocity at which the MDF detonates.
One problem that arises is that the velocity of detonation (VOD) for MDF may change over time. Such a change would change the actuation delay for devices such as ordinance that typically have a long shelf life between date of manufacture and date of use. For a quality check, VOD can be measured in a laboratory after the MDF is removed from a few stored devices. The average VOD for these devices is imputed to the remaining stored devices. However, handling the MDF introduces another variable that is not present in the stored devices, so the accuracy of this test is not certain.